The invention relates to the use of thermoplastic liners for disposition within pipe lines, either initially or as a repair. In the case of new piping, the liner will protect the internal walls from deterioration, and the liner can be replaced from time to time. In the case of deteriorated or damaged piping, the liner will restore the fluid transporting capability of the pipeline and will prevent further interior deterioration. The thermoplastic pipe liner is a stand-alone product capable of carrying the mechanical forces of the piping system. The use of such a liner is presented in my previous patents, U.S. Pat. Nos. 4,863,365, 4,985,196, 4,986,951, 4,998,871, 5,091,137, 5,112,211, and 5,342,570, which teach the general concept of a deformed liner and field application for insertion into, and subsequent reshaping to its original extruded form, within the pipe as a liner. In the case of polyethylene material, the extruded tube is deformed at a temperature equal to or higher than 160.degree. F. (crystalline point) whereat a secondary temporary shape can be maintained. In the case of PVC or PVC/Pe copolymer, the round extrudate is directly shaped into a deformed cross-section during the first cooling stage of the production line. In all cases, heat and deforming tools are required to obtain a deformed collapsed shape. The same applies during the reforming of the liner within the pipe. Heat transfer and pressure are applied to the deformed liner to erase the temporary shape and reform the liner to its original round shape. Thermoplastic materials have a high thermal coefficient of expansion. During the manufacturing and installation processes, the liner is subjected to high variations of temperature, forcing the material to expand both axially and radially. When the liner is cooled back down to ambient temperature under pressure to lock it in place, stresses are induced which cause the liner to shrink after a certain period of time. The shrinkage of the liner creates a gap between the liner and carrier pipe that can facilitate unwanted water migration in sewer and drain lines or trap gases in industrial and gas lines.
The axial shrinkage of the liner can create tremendous axial stress forces in a free-span portion of the liner. For example, in a sewer line installation with house service line connections to be reopened after lining, if the liner is free-span (no interlocking circumferential areas with the carrier pipe), the liner can develop a total circumferential crack during the cutting operation causing a full separation of several inches, or the liner can move axially, in which case the opening does not match the service line, and the flow from the house is blocked. Even in state of the art sliplining wherein smaller round polyethylene pipe is inserted into the sewer line, the shrinkage phenomenon is known and has been reported in many articles and papers. In this instance, the shrinkage comes from the extrusion process. During the extrusion process, the melted thermoplastic material is pushed through a die and tip tooling by a rotating compression screw. As a result, the extruded pipe has a angular motion up to 90 degrees per 20 to 30 feet of length which is locked into the material by the cooling process. In order to obtain the desired pipe diameter and wall thickness, the extrudate is drawn down by axial pulling, thus inducing axial and radial stresses.
It is a general object of the this invention to provide a method for producing a temporarily deformed pipe liner from extruded thermoplastic round pipe of tubular cross-section for insertion into a pipe or conduit and reformation of the deformed pipe liner to the original extruded tubular cross-section without inducing heat transfer stresses, which inventive method will eliminate the existing axial and radial stresses in extruded thermoplastic round pipe as well as any residual stresses due to butt-fuse bonding segments of extruded thermoplastic round pipe to achieve a required continuous length.
This new method for producing pipe liners described herein involves a first step of annealing the stresses induced in the extruded thermoplastic round pipe. A novel feature of this method is raising the thermoplastic pipe wall thickness temperature to a maximum of 150.degree. F. to relax the material, then slowly cooling the thermoplastic pipe wall thickness to ambient temperature to release the stresses. Releasing the extrusion stresses facilitates the manufacturing process, since the pipe will no longer have a tendency to rotate and slip out of the rollers during the subsequent deforming process.
After annealing, and now at ambient temperature, the thermoplastic pipe liner enters the deformation process and the end which first enters the deformation process line is sealed and an internal vacuum is applied to the pipe liner to collapse the round pipe liner to a flattened ribbon shape. In order to apply and maintain the vacuum, a multi-pig is inserted inside the pipe liner from the tail end of the pipe. The pig is filled with hydraulic fluid to obtain 100% vacuum sealing in the pipe liner as it enters the deformation process. The round pipe liner enters a set of four pig-stopping rollers which alter the pipe liner from a round shape to a square shape. The purpose of these pig-stopping rollers is to stop and trap the multi-pig at a fixed position by reducing the pipe liner cross-section as the pipe liner is drawn forward through the deforming process. The suction of the applied vacuum will also draw the pig. From that fixed position, at a distance of 15 to 30 times the pipe liner diameter, a set of two flattening rollers collapse the pipe liner into a flattened ribbon shape. Farther down the line, a second set of two bending rollers fold the flattened ribbon shape into a deformed "U" shape thereby creating a temporarily deformed pipe liner. Under the vacuum, the deformed pipe liner cannot regain its round shape. In heavy wall thickness pipe liner where the spring effect forces are greater than the vacuum forces, strapping of the deformed pipe liner may be required. The deforming process is performed at a pipe liner wall thickness temperature of 100.degree. F., at which the thermoplastic material has most of its mechanical strength properties and, therefore, can accept the mechanical deforming process without locked-in elongation stresses being induced. In the case of water and gas line liners, hydraulic fluid, or any like oil base material, cannot be used with the poly pig. To obtain 100% sealing, the number of sealing elements of the poly-pig may have to be increased.
It is also contemplated that the pipe liner may be produced in a continuous length greater than the conduit to be repaired. In this case, if a continuous extruded length of round thermoplastic pipe is not available in adequate lengths, it may be necessary to butt-fuse weld individual segments of anywhere from 20 feet to 50 feet in length in order to obtain the desired length. This welding process is another source of stress which will be relieved by the annealing process.
Another novel feature of this invention is in sewer/drain line applications where groundwater infiltration needs to be eliminated. As previously mentioned, any liner system using thermoplastic materials or thermo-setting resins is subjected to great variations in temperature during the installation process. As a result, after a certain period of time, radial shrinkage occurs which allows groundwater to flow back into the sewer line at any openings such as house connections. The new feature is to apply a specially designed grout into the inner fold of the deformed "U" cross section during the deforming process. This grout is a hydrophobic or hydrophobic polyurethane material of high viscosity which retains its properties at a temperature greater than 150.degree. F. and can absorb 8-10 times its volume of water. After the deformed pipe liner has been inserted into a pipe or conduit and during the process of re-rounding or reforming the pipe liner to its original tubular cross section, the grout flows around the outer surface of the pipe liner sealing the gap between the pipe liner and conduit. During expansion of the pipe liner, the grout penetrates cracks and opened joints in the conduit sealing the complete system. When the grout comes in contact with water it turns into a foam. Due to its thermal expansion coefficient, the pipe liner might shrink, but the grout will compensate for any shrinkage and keep the system sealed.
At the start-up of the deformation process, the end of the pipe liner to first enter the process is sealed by a 450.degree. F. molding press at a pressure of 100 bars. An electro-fused saddle coupling is installed on one side of the pipe liner near the sealed end and connected to the vacuum pump via a shut-down valve. At the other end of the deformed pipe liner segment, a pulling head is inserted in the inner-fold and the liner is thermo-sealed by fusion at a temperature of 450.degree. F. and a pressure of 100 bars, whereby the pulling head becomes part of the pipe liner.
Once the desired length of temporarily deformed pipe liner has been produced and sealed as above described, it is packaged on a reel or coiled. Another novel feature of this process is that the applied vacuum pre-stresses the pipe liner, allowing it to be bent on a smaller radius. Thermoplastic material cannot withstand much axial compression. As a result, the pipe liner, as well as a round pipe, will buckle when the compression forces due to the bending are greater than the compression forces the material can support. Maintaining the applied vacuum axially compresses the material and creates a pre-stress condition whereby the difference between the area under compression versus the area under elongation is minimized, increasing the inert cross-section. Consequently, the pipe liner can be bent on a much smaller radius without buckling, therefore larger size pipe liner can be coiled and packaged in sizes transportable by common carrier. For smaller size pipe liner, longer continuous lengths can be coiled on a regular size reel.
At the job site, once the pipe liner is threaded by a pulling winch through the conduit to be repaired, the pulling head is severed at the downstream end to release the vacuum. At the upstream end, the thermo-seal plug is cut off. The pipe liner regains its original round shape by itself but will be locked by the carrier pipe in a somewhat deformed configuration. End-fitting couplings are attached to both ends of the pipe liner, and a soft-pig is propelled by pressurized air through the entire length to re-round the pipe liner. During re-rounding of the pipe liner in a sewer line rehabilitation, the hydrophilic/hydrophobic grout material flows freely around the pipe liner turning to foam when it comes into contact with water, thus sealing the gap between the pipe liner and carrier pipe or conduit. Steam is then introduced into the pipe liner to mold it to the internal contours of the carrier pipe or conduit. The hydrophilic/hydrophobic foam is squeezed into cracks and openings. The pipe liner is cooled down slowly by air to ambient temperature. The amount of shrinkage due to heat transfer is minimized compared to other pipe lining systems that depend solely on heat to unfold the pipe liner.
In previous pipe liner systems, if there is cold water present in the conduit to be repaired (i.e. low spot or active service line), the pipe liner material is not uniformly subjected to temperature elevation. When pressure is applied to unfold the pipe liner, the hottest part of the pipe liner cross-section will unfold and elongate and, over time, considerable shrinkage will occur. In this new pipe lining system, since the pipe liner is unfolded at ambient temperature, there is no thermal expansion.
In the case of sewer and drain lines where the inside diameter of the conduit has large variation, the pipe liner has an outside diameter slightly smaller than the conduit's inside diameter. The liner needs to be expanded to obtain a tight fit and minimize the gap between the pipe liner and the conduit. In the case of pressure pipe application, the pipe liner's outside diameter can be manufactured more precisely, since there is significantly less variation to the inside diameter of the conduit. In this application, the pipe liner does not need to be molded to the contours of the conduit, and the hydrophilic or hydrophobic material is not needed.